After the piston failed many pieces of aluminum were collected from the sump and the crankcase, flywheel oil purifier and oil pipes flushed with solvent. I had hoped that aluminum shards, being 3x denser than oil, would settle in the sump and that the sump's very efficient gauze strainer would catch any I missed but within a mile or two the return pump failed and the Ariel was laying a smokescreen through the neighborhood. So all the oil was dumped and replaced and the pump stripped and cleaned again.
The Norton ride shortly after switching to the magneto
This seemed sufficient for many months including a 100-mile ride with the Norton club but, at the end of May, on a fast ride with friends, it erupted another toxic smokescreen. I tried to clear the return pump at the side of the road but was unable to and the bike fouled my last plug a mile from home. The sump was drained and the gauze cleaned. Two days later it did it again and a friendly guy gave me a ride home.
The whole oiling system was stripped - oil tank and pipes flushed with solvent, cylinder head and cambox pulled and cleaned out (surprised to find aluminum flakes in the cam box), big end bearing flushed with clean oil and flywheel oil purifier flushed again, gauze strainers cleaned and adjusted to close up any gaps.
I also took the precaution of cleaning and lubing an old oil pump, wrapping it in a soft rag with all the correct tools, enclosing that in a heavy ziplock bag and putting that in the toolbox. After a couple weeks of ever longer rides I had the confidence to make a 120 mile trip to the mountains. I also wanted to check to see if the carb was too rich to run at altitude.